Post Harvest

Stubborn disease of citrus, caused by Spiroplasma citri, is an important disease of citrus in the hot, arid inland areas of California and Arizona. The two methods most commonly used for detection of stubborn have been biological indexing and culture in a cell-free medium. Indexing for stubborn disease of citrus is difficult since it requires the somewhat tricky side-graft or leaf vein method, and it takes several months to obtain results. Culturing is also somewhat time consuming, sometimes requires several attempts, and can produce false positives from contamination. Culturing is the test of record for CDFA and most regulatory agencies.

Magnetic Resonance Imaging (MRI) has proven to be a valuable medical diagnostic tool for investigating damage in humans. This tool is useful in medicine since it provides information on “soft tissues” in the body such as muscles and tendons. Our project was focused on developing magnetic resonance for use in detecting damage to “soft tissues” in oranges.

The goal of this research was to reduce economic losses to the lemon industry due to postharvest decay and to increase postharvest quality and storage life of lemons using the inexpensive naturally-occurring compounds spermidine, spermine and salicylic acid applied as a dip or drench after washing or in the storage wax. If successful, the research would identify a less-expensive material that is as effective or more effective than GA3 combined with 2,4-D.

The goal of the robot harvester project’s second phase, FY2004-2005, was to begin to validate Vision Robotics’ concept for mapping orange trees using the scout robot. The scout will map the grove determining the tree locations, the number and size of the oranges and their approximate positions on each tree. Once a tree and its oranges are mapped, the scout will determine a picking-plan for that tree, which it will transmit to a harvester robot.

During the second year of this project, we continued the work initiated last year. This project uses the sensory panel volunteers at the UC Kearney Ag Center to evaluate early season navel oranges with the intent to develop a database of the relationship between SSC/TA ratio, volatiles, and acceptability of navel orange fruit. Additionally, during this year we explored the relationship between fruit handling practices, waxes and fruit acceptability following storage.

This research investigates the efficacy of ozone combined with carbon dioxide and vacuum to control bean thrips in navel oranges. A focus of this work in 2004-2005 was effects of wax type and cultivar to mitigate phytotoxic damage.

The goal of this project is to develop and test a field method for using an ethanol sensor to measure whether a sample of oranges contains a threshold level of freeze-damaged fruit. The citrus industry is seeking an objective alternative to the manual inspection method used by CDFA inspectors to determine freeze damage in navel oranges.

The purpose of this project is to develop new methods to control postharvest decay of citrus for use in California packinghouses. Practical experiments with the newly approved postharvest fungicide pyrimethanil (PYR) were completed in 2005. PYR has recently been approved for use in California to control green mold, caused by Penicillium digitatum, though acceptance of its residues in some overseas markets is still in progress.

In the summer of 2005, fludioxonil and pyrimethanil were registered in California following the federal registration in the fall of 2004 for postharvest use on citrus. The postharvest registration of azoxystrobin is still pending but is expected in the summer of 2006. In Sept. 2005, we successfully placed propiconazole into the federal IR-4 program to establish a residue tolerance for postharvest use, and these studies are planned for 2006.

Vision Robotics (VRC) has demonstrated that it is possible to see all the oranges (>99%) on trees in production groves from somewhere outside the tree canopy. In practice, this requires a thorough scan of the tree canopy, and the closer to the canopy and wider the viewing angle the better.